The sun still shined on Westwood Boulevard, the thrumming commercial heart of the biggest Iranian community outside Iran.

Families lunched on chicken kabob at Flame, Shaherzad and other restaurants. Students browsed titles in Farsi bookstores. Music lovers flicked through CDs of Ebrahim “Ebi” Hamedi, the king of Persian pop.

Just another Saturday in Tehrangeles, a portmanteau of Tehran and Los Angeles coined by exiles and their descendants – also known as Little Persia, a term so well established Google Maps recognises it.

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The apparent normality deceived. In hushed and bewildered tones, people wondered whether they still recognised the United States, the adopted homeland that had welcomed and sheltered them but now labelled them potential terrorists.

“It is totally unjust. This will affect thousands and thousands of families that are completely innocent,” said Siamak, a 56-year-old physician who fled Iran after the ayatollahs took over in 1979. “We ourselves are victims of terrorism. Now we are branded terrorists?”

The order, named the Protection of the Nation from Foreign Terrorist Entry into the United States, imposes a a 90-day block on entry from citizens from Iran, Iraq, Syria, Yemen, Sudan, Libya and Somalia.

Iran’s foreign affairs ministry said it will take legal, political and reciprocal measures.

Overnight, many of the up to 500,000 Iranians and Iranian Americans who live in southern California felt as though the US border had clanged shut. If they leave, they may not be able to return. Those who are currently outside the US – even those with green cards and visas – are marooned.

“My friend is visiting relatives in Tehran and now he’s stuck,” said a young bookseller, who like most interviewees did not want her name published. “He’s got a job here, a mortgage, car payments. What will happen to him?”

The question hung over every family with noncitizen relatives abroad. “It’s ridiculous,” said Sam, a restaurant manager. “We’ve felt good here. California is very open-minded. But now this.…” His voice trailed off.

The director Ashgar Farhadi, who won an Oscar in 2012 for his film A Separation, and is nominated again for The Salesman, may not be able to attend next month’s ceremony, an absence which would fuel Hollywood’s animus towards the Trump administration. The Academy of Motion Picture Arts and Sciences called the prospect “extremely troubling”.

One middle-aged woman, loading groceries into a Porsche, quivered with indignation. “Iranians are not murderers. Iranians are not terrorists. Americans should know that.” She said “sanity” would return. “Trump is not going to last so long. They’ll impeach him.”

Trump had promised a crackdown during the campaign but the executive order still came as a shock. California’s Iranians, who often prefer the term Persian to distance themselves from Iran’s current leadership, form a thriving community with roots stretching back decades. Some arrived as students in the 1960s, followed by waves of exiles after the 1979 revolution.

Muslims tended to settle in Orange Country and the San Fernando valley, Jews in Westwood and Beverly Hills.

Anecdotal evidence suggests many Jewish Iranians voted for Trump because he strongly backed Israel and bashed Tehran’s rulers. Some are unrepentant.

“Yes, Trump!” said one 70-year-old man who gave his name only as Kevin. “He will stop the terrorists. You know when you leave your house, you lock the door, right? He’s doing right.”

Asked whether a blanket ban on Iranian citizens was a good idea, Kevin hesitated. “All, maybe not. But you have to lock your house.”

Hassan Ali, a 29-year-old engineer from Pakistan who was buying pepper in Tehran Market, said targeting Muslims or any other religion was un-American. “This country is supposed to be a melting pot.”

The executive order seemed to have a chilling, immediate effect. Of 16 people of Iranian heritage interviewed at random in west LA, not one was willing to have their full name published.

Holly Dagres, a Middle East commentator, discovered the same reluctance among her contacts. “Iranians are scared to share.”

The community in Tehrangles learned to keep its head down during the hostile atmosphere engendered by the 1979 hostage crisis. Embracing the term Persian – evoking carpets, cats and antiquity – was a way to avoid connotations of terrorism and fanaticism.

But that linguistic sidestep did not deflect Trump, said Siamak, the physician. “He has branded us. The stereotype is back. I fear things will get worse and worse.”